Comparative Metabolic Defense Responses of Three Tree Species to the Supplemental Feeding Behavior of Anoplophora glabripennis

<i>Elaeagnus angustifolia</i> L. can attract adult Asian longhorned beetle (ALB), <i>Anoplophora glabripennis</i> (Motschulsky), and kill their offspring by gum secretion in oviposition scars. This plant has the potential to be used as a dead-end trap tree for ALB management. However, there is a limited understanding of the attraction ability and biochemical defense response of <i>E. angustifolia</i> to ALB. In this study, we conducted host selection experiments with ALB and then performed physiological and biochemical assays on twigs from different tree species before and after ALB feeding. We analyzed the differential metabolites using the liquid chromatograph-mass spectrometer method. The results showed that ALB's feeding preference was <i>E. angustifolia</i> > <i>P.× xiaohei</i> var. <i>gansuensis</i> > <i>P. alba</i> var. <i>pyramidalis</i>. After ALB feeding, the content of soluble sugars, soluble proteins, flavonoids, and tannins decreased significantly in all species. In three comparison groups, a total of 492 differential metabolites were identified (<i>E. angustifolia</i>:195, <i>P.× xiaohei</i> var. <i>gansuensis</i>:255, <i>P. alba</i> var. <i>pyramidalis</i>:244). Differential metabolites were divided into overlapping and specific metabolites for analysis. The overlapping differential metabolites 7-isojasmonic acid, zerumbone, and salicin in the twigs of three tree species showed upregulation after ALB feeding. The specific metabolites silibinin, catechin, and geniposide, in <i>E. angustifolia,</i> significantly increased after being damaged. Differential metabolites enriched in KEGG pathways indicated that ALB feeding activated tyrosine metabolism and the biosynthesis of phenylpropanoids in three tree species, with a particularly high enrichment of differential metabolites in the flavonoid biosynthesis pathway in <i>E. angustifolia</i>. This study provides the metabolic defense strategies of different tree species against ALB feeding and proposes candidate metabolites that can serve as metabolic biomarkers, potentially offering valuable insights into using <i>E. angustifolia</i> as a control measure against ALB.